<p>This paper proposes a similar design method for the torque transmission capacity of interference fit in order to experimentally test their torsional capacity using a similar model instead of the actual structure. Based on the similitude theory, the similarity criterion for the torque transmission capacity of the interference fit is derived, and the influence of the similarity criterion distortion on the torque transmission capacity of the similarity model is discussed. Taking the interference fit between the gear bushing and the front journal of a real aero-engine as an example, finite element analysis (FEA) were performed to verify the similarity ratio of the torque transmission capacity of scaled models. By optimizing the case structure dimensions using the similarity criterion distortion reduction method, a partially similar model was established. The torque transmission capability prediction coefficient between the partially similar model and the prototype was 0.972, indicating that the partially similar model effectively reflect the torque transmission capacity of the prototype. Experiments on the torque transmission capacity of interference fit were conducted on partially similar model with different interference. By incorporating the experimentally calibrated maximum static friction coefficient, the comparison of theoretical and test results verifies the correctness of the similarity design method for interference fit torque transmission capacity proposed in this paper. This method has engineering practicality and provides a reference for the design of similarity test of torque transmission capacity of the interference fit.</p>